Single pixel camera

ABSTRACT

A camera system includes a single pixel photo-sensor disposed in or on a substrate to acquire image data. A micro-lens is adjustably positioned above the single pixel photo-sensor to focus external scene light onto the single pixel photo-sensor. An actuator is coupled to the micro-lens to adjust a position of the micro-lens relative to the single pixel photo-sensor. A controller controls the actuator to sequentially reposition the micro-lens to focus the external scene light incident from different angles onto the single pixel photo-sensor. Readout circuitry is coupled to sequentially readout the image data associated with each of the different angles from the single pixel photo-sensor.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.61/695,007 filed on Aug. 30, 2012, the contents of which areincorporated herein by reference.

TECHNICAL FIELD

This disclosure relates generally to camera modules, and in particularbut not exclusively, relates to integrated image sensors.

BACKGROUND INFORMATION

As the popularity of portable computing spreads, the demand for compactdevices, such as smart phones, head mounted display (“HMDs”), tablets,laptops, etc., increases. To meet this demand, it is important tocontinue to shrink the form factor of internal components of theseportable computing devices. One such internal device is a camera module.

Convention camera modules consist of a lens system and image sensorhaving a finite number of pixels. The resolution of the image capturedby the camera module is determined by the pixel count of the particularimage sensor. For example, a 5 mega-pixel image sensor with 1.75-umpixels has an active image area (pixel array) of about 4.6 mm×3.4 mm,while the whole image sensor die is approximately 5.75 mm×5.75 mm. Thisrequires a lens system having a diagonal size of about 5.4 mm (oftendetermined by the size of the last lens element in the lens system) soas to cover the whole image field on the image sensor. With thethickness of the lens barrel and camera holder, the horizontal dimensionof the camera module extends to approximately 7.5 mm. Furthermore, toaccommodate the finite resolution of the image sensor, the lens systemoften needs to include several lens elements stacked on top of eachother to correct for optical aberrations to achieve a reasonable opticalresolution across the whole image field. This lens stacking contributessignificantly to the vertical height of the camera module.

As can be seen from the above discussion, the overall camera module sizein all three dimensions is substantially determined in part by the sizeof the image sensor die. Therefore, one way to miniaturize a cameramodule is through reducing the size of the image sensor die.Conventionally, this size reduction has been achieved by shrinking thesize of the individual pixels in the pixel array while maintaining orincreasing the pixel count of the overall image sensor. However, thereare a number of disadvantages to this miniaturization approach.

First, smaller pixel sizes impose significant challenges in the designand manufacturing of the camera lens system. As pixel sizes decrease,there must be a corresponding increase in the optical resolution of thelens system to maintain the image quality (e.g., sharpness). Second,smaller pixel sizes decrease the image sensor sensitivity and oftensacrifice low-light performance for size and resolution. Third, there isa practical limit in the physical size to which a pixel can be shrunk.Pixels are already approaching this threshold, despite continued demandfor increasingly smaller camera modules.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments of the invention aredescribed with reference to the following figures, wherein likereference numerals refer to like parts throughout the various viewsunless otherwise specified. The drawings are not necessarily to scale,emphasis instead being placed upon illustrating the principles beingdescribed.

FIG. 1 is a functional block diagram illustrating components of a singlepixel camera system, in accordance with an embodiment of the disclosure.

FIG. 2 is a flow chart illustrating operation of a single pixel camerasystem, in accordance with an embodiment of the disclosure.

FIGS. 3A and 3B illustrate a single pixel camera module, in accordancewith an embodiment of the disclosure.

FIG. 4 illustrates operation of a two-dimensional scanning actuator, inaccordance with an embodiment of the disclosure.

FIG. 5 illustrates operation of a scanning actuator that moves themicro-lens along an arc path to acquire external scene light incident atdifferent angles, in accordance with an embodiment of the disclosure.

FIG. 6 illustrates how multiple single pixel camera modules can beintegrated onto a common semiconductor die, in accordance with anembodiment of the disclosure.

DETAILED DESCRIPTION

Embodiments of an apparatus and method of operation for a single pixelcamera module are described herein. In the following descriptionnumerous specific details are set forth to provide a thoroughunderstanding of the embodiments. One skilled in the relevant art willrecognize, however, that the techniques described herein can bepracticed without one or more of the specific details, or with othermethods, components, materials, etc. In other instances, well-knownstructures, materials, or operations are not shown or described indetail to avoid obscuring certain aspects.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the present invention. Thus, theappearances of the phrases “in one embodiment” or “in an embodiment” invarious places throughout this specification are not necessarily allreferring to the same embodiment. Furthermore, the particular features,structures, or characteristics may be combined in any suitable manner inone or more embodiments.

FIG. 1 is a functional block diagram illustrating components of a singlepixel camera system 100, in accordance with an embodiment of thedisclosure. The illustrated embodiment of single pixel camera system 100includes a single pixel photo-sensor 105, a micro-lens 110, an actuator115, readout circuitry 120, buffer memory 125, and a controller 130.

Single pixel photo-sensor 105 may be implemented as acomplementary-metal-oxide-semiconductor (“CMOS”) photo-diode (e.g., aP-I-N photo-diode, an avalanche photo-diode, or otherwise), a chargecoupled device (“CCD”), or other photo-sensitive devices capable ofcapturing image data. In order to provide good low light sensitivity andlarge full well capacity and extended dynamic range, single pixelphoto-sensor 105 may be implemented with a relatively largephoto-sensitive area. For example, in the case of a photo-diode, singlepixel photo-sensor 105 may be on the order of 10 μm to 100 μm. Ofcourse, other sizes may be implemented as well.

Various different angles of incidence 135A, 135B, 135C of external scenelight are sequentially brought to a focus on single pixel photo-sensor105 by micro-lens 110. Micro-lens 110 may be implemented usingrefractive, diffractive, or hybrid lens types. Micro-lens 110 may bedesigned to have a depth of field (“DOF”) that extends out to infinity.In this case, micro-lens 110 is configured to focus substantiallycollimated light onto single pixel photo-sensor 105. In one embodiment,micro-lens 110 is implemented as a clear or pigmented polymer materialusing photolithography and reflow techniques. In another embodiment,micro-lens 110 is implemented in plastic using injection moldingtechniques. In yet another embodiment, micro-lens 110 is a liquid lens.Of course, other lens technologies, materials, and fabricationtechniques may be used.

Actuator 115 is coupled to micro-lens 110 to adjust its position tofocus external scene light incident from different angles onto singlepixel photo-sensor 105. In one embodiment, actuator 115 is atwo-dimensional (“2D”) actuator capable of translating micro-lens 110along two independent axes (e.g., x and y). Offsetting micro-lens 110from center alignment with single pixel photo-sensor 105 along a flatplane causes different angles of incidence to be selectively focusedonto single pixel photo-sensor 105 at a given time. In one embodiment,actuator 115 is a three-dimensional (“3D”) actuator capable oftranslating micro-lens 110 along three independent axes (e.g., x, y, z).A 3D actuator having a z-component adjustability to change theseparation distance between micro-lens 110 and single pixel photo-sensor105 could provide a variable DOF. In other embodiments, actuator 115 mayconstrain the movement of micro-lens 110 along an arc-like path thattilts micro-lens 110 with x and y displacements from center. Forexample, when micro-lens 110 is moved left to focus external scene lightwith incident angle 135C onto single pixel photo-sensor 105, micro-lens110 is also tilted towards this angle. Tilting micro-lens 110 such thatits central axis faces towards the direction of incident external scenelight may increase the quantum efficiency of the system, since a greaterportion of incident light can be captured by single pixel photo-sensor105. Actuator 115 may be implemented using a variety of differenttechnologies including micro-electro-mechanical systems (“MEMS”),electrical comb drivers, piezoelectric crystals, thermally expandingmaterials, shape memory alloys, electro-static capacitive actuators,magnetic actuators, etc.

Readout circuitry 120 may include a number of sub-components including asignal amplifier, correlated double sampling circuitry, and ananalog-to-digital converter (“DAC”). The signal amplifier may be aconventional or differential amplifier for amplifying the analog outputsignal from single pixel photo-sensor 105. The correlated doublesampling circuitry may be used to achieve a dark signal offset in theimage data. The DAC converts the analog image signal to digital imagedata (pixel data), which is output from readout circuitry sequentiallyone pixel Px at a time.

Buffer memory 125 may include volatile memory (e.g, SRAM, DRAM, etc.),non-volatile memory (e.g., NAND or flash memory, etc.), or hardwareregisters for temporarily buffering the sequential stream of image dataoutput from readout circuitry 120. In one embodiment, buffer memory 125is large enough to store at least one entire image frame 140 of pixeldata along with metadata indicating how to order the pixel data into a2D image frame. In one embodiment, the metadata may be actual datastored along with each unit of pixel data. Since the pixel data issequentially output from readout circuitry 120 in a consistent andrepeated pattern, in one embodiment, the metadata is stored in the orderin which the pixel data is stored within buffer memory 125. As such, inthis embodiment, pixel data may simply be stored in a linear buffer. Ifsingle pixel camera system 100 is capable of selectively acquiringdifferent image resolutions, then the resolution setting may also bestored in buffer memory 125 so that the pixel data can be appropriatelyreassembled when output from buffer memory 125.

In the illustrated embodiment, controller 130 is coupled to each ofactuator 115, single pixel photo-sensor 105, readout circuitry 120, andbuffer memory 125 to coordinate their operation. Controller 130 may beimplemented by software/firmware instructions executed on amicroprocessor, implemented entirely in hardware logic (e.g., ASIC,FPGA, etc.), or a combination of both. Controller 130 outputs controlsignals to actuator 115 to select a given position for micro-lens 110.The control signals output from controller 130 to single pixelphoto-sensor 105 may include a reset signal to reset the photo-sensorbetween image acquisition windows, a shutter signal to commence imageacquisition, and a transfer signal to transfer the image charge to aninternal storage node for biasing an output transistor. In oneembodiment, controller 130 is coupled to readout circuitry 120 toindicate when the analog image signal output from single pixelphoto-sensor 105 is valid and to acquire a black level signal fromsingle pixel photo-sensor 105 for correlated double sampling. In theillustrated embodiment, controller 130 is further coupled to buffermemory 125 to control output of the pixel data off-chip as an image fileor image frame 140.

In one embodiment, the functional components of single pixel camerasystem 100 illustrated in FIG. 1 may be integrated onto a singlesemiconductor die. Wafer level fabrication techniques may be used tofabricate many instances of system 100 on a wafer, which are then dicedand packaged. For example, micro-lens 110 may be fabricated using UVreplicating technology, while the circuit components of single pixelphoto-sensor 105, controller 130, readout circuitry 120, and buffermemory 125 may be implemented using conventional CMOS technologies. Inthe case of MEMS technologies, actuator 115 may also be fabricated onthe same die using compatible semiconductor fabrication techniques.

FIG. 2 is a flow chart illustrating a process 200 for operation ofsingle pixel camera system 100, in accordance with an embodiment of thedisclosure. The order in which some or all of the process blocks appearin process 200 should not be deemed limiting. Rather, one of ordinaryskill in the art having the benefit of the present disclosure willunderstand that some of the process blocks may be executed in a varietyof orders not illustrated, or even in parallel.

In a process block 205, actuator 115 is configured by controller 130 toadjust the position of micro-lens 110 to select a given angle ofincidence of external scene light. In a process block 210, single pixelphoto-sensor 105 is reset to erase any image charge remaining from theprevious image acquisition cycle. Resetting the photo-sensor may includecoupling the photo-sensor to a default voltage. Once reset, imageacquisition (photo-generated charge integration) can commence to acquirethe image charge for the current image pixel (process block 215). Afterthe acquisition window is complete, an analog image signal is read intoreadout circuitry 120 (process block 220). In one embodiment, duringreadout, readout circuitry 120 amplifies the analog image signal,offsets the black level, and converts the analog image signal to digitalimage data (pixel data). In process block 225, the current pixel data isbuffered into buffer memory 125. If the complete image frame has not yetbeen acquired (decision block 230), then the current image pixel isupdated (process block 235) and process 200 returns to process block 205where the position of micro-lens 110 is re-adjusted. In one embodiment,while micro-lens 110 is being repositioned to acquire the next imagepixel, the charge on single pixel photo-sensor 105 is being reset inanticipation of acquiring the next image pixel data. Loop 237 continuesuntil an entire/complete image frame is acquired (decision block 230).Once an entire image frame is buffered in buffer memory 125, thecomplete image can be assembled into an image file format and outputoff-chip (process block 240). Thus, actuator 115 and controller 130sequentially readjust the position of micro-lens 110 to scan througheach angle of incidence one pixel at a time to focus light fromdifferent spatial points in the external scene. In other words, in oneembodiment, actuator 115 raster scans micro-lens 110 through eachposition of a single image frame. The raster scan may follow a varietyof different sweeping patterns including scanning rows, scanningcolumns, diagonal scanning, left-to-right scanning, right-to-leftscanning, left-to-right-to-left and repeat scanning, a clockwise orcounterclockwise spiral scan, or otherwise. The term “raster scan” isused broadly herein to refer to a sweeping motion that traces out allimage pixel locations in an image frame in any pattern. Depending uponthe type of actuator, a per pixel scan frequency of 100 Hz to 0.1 GHzmay be achievable, making video images realizable.

FIGS. 3A and 3B illustrate a single pixel camera module 300, inaccordance with an embodiment of the disclosure. FIG. 3A is across-sectional view of single pixel camera module 300 while FIG. 3B isa plan view of the same. Single pixel camera module 300 is one possibleimplementation of single pixel camera system 100. The illustratedembodiment of single pixel camera module 300 includes a substrate 305(e.g., semiconductor die), a photo-sensor 310, a micro-lens 315, anactuator 320, and a housing 325. The other control system elementsincluding readout circuitry, buffer memory, and a controller are notillustrated in FIGS. 3A and 3B; however, these elements can beintegrated into/onto substrate 305 using CMOS technologies.

Actuator 320 represents one possible 2D scanning actuator that iscapable of adjusting a position of micro-lens 315 in a 2D x-y plane viacontraction/expansion of connecting members 330 via electro-staticforces. In the illustrated embodiment, micro-lens 315 is encapsulated(e.g., hermetically sealed) within a vacuum by a transparent housing325. The vacuum reduces drag associated with quick motions through airand prevents dust or debris from obstructing or jamming actuator 320.

FIG. 4 illustrates a single pixel camera module 400, in accordance withan embodiment of the disclosure. Single pixel camera module 400 isanother possible implementation of a 2D scanning actuator version ofsingle pixel camera system 100. Only the micro-lens 405 and actuatorcomponents: flexible members 410 and adjustable anchors 415 areillustrated so as not to clutter the drawing; however, it should beappreciated that the remaining components of single pixel camera system100 are also integrated into the system. During operation, adjustableanchors 415 are actuated to move left or right, which in turn compressesor stretches flexible members 410, thereby selectively moving micro-lens405.

The center depiction illustrates single pixel camera module 400 at itsdefault resting position. To move micro-lens 405 upwards along the +ydirection, both left and right anchors 415 are moved inward (seedepiction 420). To move micro-lens 405 downwards along the −y direction,both left and right anchors 415 are moved outward (see depiction 425).To move micro-lens 405 right along the +x direction, both left and rightanchors 415 are moved to the right (see depiction 430). To movemicro-lens 405 left along the −x direction, both left and right anchors415 are moved to the left (see depiction 435). Anchors 415 may beactuated using a variety of techniques including electro-staticcapacitive plates, piezoelectric crystals, or otherwise.

FIG. 5 illustrates operation of a scanning actuator 500 that moves amicro-lens 505 along an arc path 510 to acquire external scene lightincident at different angles, in accordance with an embodiment of thedisclosure. As discuss above, actuating micro-lens 505 in a manner thatfacilitates tilting micro-lens 505 towards the direction of the incidentlight can serve to increase quantum efficiency the image sensor bycapturing and focusing more light onto single pixel photo-sensor 515.Arc path 510 may implemented using one or more tracks that guidemicro-lens 505 and follow a curved path.

FIG. 6 illustrates how multiple single pixel camera modules 600 can beintegrated onto a single common semiconductor die 605, in accordancewith an embodiment of the disclosure. In one embodiment, a color imagesensor is achieved by including a different color filter (e.g., red,green, blue) with the micro-lens of each camera module 600. The scannedimages acquired by each camera module 600 can then registered/aligned toeach other and combined to generate a color image frame. In oneembodiment, each camera module 600 can be assigned to scan out differentspatial coordinates of an external scene. The different spatialcoordinates correspond to different portions of a single composite imageframe. After a calibration to align the constituent portions of theimage frame, the image data from each camera module 600 could then bestitched together to generate a single complete image frame. This divideand conquer approach to scanning out a single image frame may be used toachieve high video frame rates. Although FIG. 6 illustrates three cameramodules 600 arranged in a line, any number of camera modules 600arranged in other patterns may be implemented.

In another embodiment, two camera modules may be positioned on the samesubstrate and have their actuators and/or controllers linked or slavedso that the respective micro-lens 110 of each camera module isrepositioned in unison to acquire stereoscopic images. In thisembodiment, the controllers would operate to synchronize the rasterscanning of the two micro-lenses while each acquires its respectiveimage frame that collectively provide depth perception or a 3D image.

The processes explained above are described in terms of software andhardware. The techniques described may constitute machine-executableinstructions embodied within a tangible or non-transitory machine (e.g.,computer) readable storage medium, that when executed by a machine willcause the machine to perform the operations described. Additionally, theprocesses may be embodied within hardware, such as an applicationspecific integrated circuit (“ASIC”) or otherwise.

A tangible machine-readable storage medium includes any mechanism thatprovides (i.e., stores) information in a form accessible by a machine(e.g., a computer, network device, personal digital assistant,manufacturing tool, any device with a set of one or more processors,etc.). For example, a machine-readable storage medium includesrecordable/non-recordable media (e.g., read only memory (ROM), randomaccess memory (RAM), magnetic disk storage media, optical storage media,flash memory devices, etc.).

The above description of illustrated embodiments of the invention,including what is described in the Abstract, is not intended to beexhaustive or to limit the invention to the precise forms disclosed.While specific embodiments of, and examples for, the invention aredescribed herein for illustrative purposes, various modifications arepossible within the scope of the invention, as those skilled in therelevant art will recognize.

These modifications can be made to the invention in light of the abovedetailed description. The terms used in the following claims should notbe construed to limit the invention to the specific embodimentsdisclosed in the specification. Rather, the scope of the invention is tobe determined entirely by the following claims, which are to beconstrued in accordance with established doctrines of claiminterpretation.

What is claimed is:
 1. A camera system, comprising: a single pixelphoto-sensor disposed in or on a substrate to acquire image data; amicro-lens adjustably positioned above the single pixel photo-sensor tofocus external scene light onto the single pixel photo-sensor; anactuator coupled to the micro-lens to adjust a position of themicro-lens relative to the single pixel photo-sensor; a controllercoupled to control the actuator to sequentially reposition themicro-lens to focus the external scene light incident from differentangles onto the single pixel photo-sensor; and readout circuitry coupledto the single pixel photo-sensor to sequentially readout the image dataassociated with each of the different angles from the single pixelphoto-sensor, wherein the image data associated with each of thedifferent angles collectively represents a single image framesequentially acquired by the single pixel photo-sensor.
 2. The camerasystem of claim 1, wherein the actuator comprises a two-dimensional(“2D”) actuator capable of translating a position of the micro-lensalong a plane in two dimensions to raster scan pixels of the singleimage frame.
 3. The camera system of claim 2, wherein the micro-lenscomprises a fixed depth of field lens.
 4. The camera system of claim 1,wherein the actuator comprises a three-dimensional (“3D”) actuatorcapable of translating a position of the micro-lens along a plane in twodimensions to raster scan pixels of the single image frame and adjustinga separation height of the micro-lens from the single pixel photo-sensorto provide a variable depth of field focus.
 5. The camera system ofclaim 1, wherein the actuator includes an arc-shaped track that guidesthe micro-lens along an arc path when displaced from a referenceposition, wherein the arc path tilts a central axis of the micro-lenstowards a direction of the external scene light as the micro-lens isdisplaced from the reference position.
 6. The camera system of claim 1,further comprising: a memory buffer to buffer the single image frameacquired sequentially by the single pixel photo-sensor.
 7. The camerasystem of claim 6, wherein the substrate comprises acomplementary-metal-oxide-semiconductor (“CMOS”) die and wherein thesingle pixel photo-sensor, the memory buffer, the controller, and thereadout circuitry are integrated onto the substrate.
 8. The camerasystem of claim 7, wherein the actuator and the micro-lens are alsointegrated onto the CMOS die.
 9. The camera system of claim 1, furthercomprising: a clear housing attached to the substrate and hermeticallysealing the micro-lens, the actuator, and the single pixel photo-sensorwithin a vacuum.
 10. The camera system of claim 1, further comprising:three camera modules disposed on the substrate and each including aninstance of the single pixel photo-sensor, the micro-lens, the actuator,the controller, and the readout circuitry, wherein each of the threecamera modules includes a different color filter to acquire a differentcolor of the external scene light.
 11. The camera system of claim 1,further comprising: a plurality of camera modules disposed on thesubstrate and each including an instance of the single pixelphoto-sensor, the micro-lens, the actuator, the controller, and thereadout circuitry, wherein the instances of the controllers areconfigured such that each camera module scans out different spatialcoordinates of the external scene light.
 12. The camera system of claim1, wherein the actuator comprises: a pair of adjustable anchors disposedon either side of the micro-lens; and flexible members coupled betweenthe adjustable anchors and the micro-lens, wherein the flexible membersare compressed or stretched by the adjustable anchors to translate themicro-lens along a first axis when the adjustable anchors translate inopposite directions to each other along a second axis substantiallyorthogonal to the first axis.
 13. The camera system of claim 1, whereinthe actuator comprises one of a micro-electro-mechanical system, anelectrical comb driver, a piezoelectric crystal, a thermally expandingmaterial, a shape memory alloy, an electro-static capacitive actuator,or a magnetic actuator.
 14. A method of operating a camera system,comprising: sequentially repositioning a micro-lens through a sequenceof positions disposed over a single pixel photo-sensor via an actuatorcoupled to the micro-lens; sequentially acquiring image signals ofexternal scene light with the single pixel photo-sensor, wherein each ofthe image signals captures an image of the external scene light incidentfrom a different angle selected via a corresponding position of thesequence of positions; and buffering the image signals acquired from thesequence of positions as an image frame.
 15. The method of claim 14,wherein the sequentially repositioning comprises raster scanning themicro-lens disposed over the single pixel photo-sensor through thesequence of positions.
 16. The method of claim 15, further comprising:buffering metadata with the image signals indicative of a raster scanpattern to facilitate assembling the image signals of the image frameinto an image file format.
 17. The method of claim 16, wherein themetadata indicates a resolution of the 2D image.
 18. The method of claim15, further comprising: raster scanning a plurality of micro-lensesdisposed over a corresponding plurality of single pixel photo-sensorsdisposed on a common substrate, wherein each of the micro-lenses scans adifferent set of spatial coordinates to capture a different portion of asingle composite image frame; and combining the image frames thatcapture a different portion of the single composite image frame by eachof the single pixel photo-sensors into the single composite image frame.19. The method of claim 14, further comprising: resetting a chargeacquired by the single pixel photo-sensor while the micro-lens is beingmoved between positions of the sequence of positions.
 20. The method ofclaim 14, wherein the single pixel photo-sensor, the micro-lens, and theactuator that moves the micro-lens are integrated onto acomplementary-metal-oxide-semiconductor (“CMOS”) die.
 21. The method ofclaim 20, wherein the single pixel photo-sensor, the micro-lens, and theactuator are hermetically sealed in a vacuum by a clear housing thatattaches to the CMOS die.
 22. The method of claim 20, wherein theactuator comprises a micro-electro-mechanical system (“MEMS”) devicethat includes a pair of adjustable anchors disposed on either side ofthe micro-lens and flexible members coupled between the adjustableanchors and the micro-lens, wherein sequentially repositioning themicro-lens includes: compressing or stretching the adjustable anchors totranslate the micro-lens along a first axis when the adjustable anchorstranslate in opposite directions to each other along a second axissubstantially orthogonal to the first axis.